1. Field of the Invention
The present invention relates to a personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction. More particularly, the present invention relates to a structure of an exhaust outlet portion of an exhaust passage extending from an exhaust port of an engine to a transom board.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The jet-propulsion personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom of a hull and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In the jet-propulsion personal watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left by operating a bar-type steering handle to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to the right or to the left.
In the jet-propulsion personal watercraft, an engine is disposed in an engine room such that a crankshaft extends along the longitudinal direction of the watercraft. The crankshaft projects rearwardly and its rear end is coupled to a pump shaft of the water jet pump, thereby driving the water jet pump.
An exhaust gas from the engine is introduced into a muffler and muffled therein, and the resulting exhaust gas is discharged outside the watercraft from an exhaust outlet that opens in a transom board at the rear end of the watercraft.
In the personal watercraft having the above configured exhaust outlet, the transom board or the like in the vicinity of the exhaust outlet is susceptible to contamination by the exhaust gas. Accordingly, the applicant disclosed an invention relating to an exhaust outlet of the watercraft, in which, by attaching an extending pipe bent obliquely downwardly at the rear end thereof to the rear end of the exhaust outlet, the contamination of the transom board by the exhaust gas is prevented and the exhaust noise is caused to contact the water surface to be reduced (see U.S. Pat. No. 6,206,741).
Although, in this structure, the exhaust noise is reduced while the watercraft is cruising at a high speed, the watercraft sometimes resonates with the water surface while cruising at a medium or low speed. With this structure, the exhaust noise is difficult to effectively reduce within a wide speed range.
The present invention addresses the above described conditions, and an object of the present invention is to provide a personal watercraft capable of preventing an exhaust gas discharged from an exhaust outlet that opens in a transom board from contaminating the transom board in the vicinity of the exhaust outlet and of reducing an exhaust noise of the exhaust gas within a wide speed range.
According to the present invention, there is provided a personal watercraft having an internal combustion engine disposed in a body thereof, for driving a water jet pump, comprising: a transom board; an exhaust outlet formed in the transom board at a rear end of an exhaust passage extending from an exhaust port of the engine to the transom board so as to open rearwardly; a flexible sheet member disposed at the exhaust outlet and having a closing portion capable of opening/closing the exhaust outlet by an exhaust pressure of an exhaust gas of the engine; and a short pipe mounted to an outside of the transom board and extending rearwardly from the transom board so as to surround the closing portion of the sheet member, for introducing the exhaust gas rearwardly.
With such a structure, the exhaust gas being discharged from the exhaust outlet formed in the transom board at the rear end of the exhaust passage extending to the transom board so as to open rearwardly is discharged outside the watercraft from a passage formed between the exhaust outlet and the sheet member by opening the closing portion of the sheet member provided in the exhaust outlet by deforming the closing portion of the flexible sheet member due to the pressure of the exhaust gas. In addition, the short pipe extending rearwardly from the transom board so as to surround the periphery of the closing portion, i.e., the short pipe surrounding the portion of the sheet member through which the exhaust gas flows and introduces the exhaust gas rearwardly, extends rearwardly from the transom board. Thereby, the exhaust gas is discharged outside the watercraft from the rear end of the short pipe located behind and apart from the transom board. As a result, the transom board is prevented from being contaminated by the exhaust gas. In addition, the exhaust noise is caused to contact the flexible sheet member and to be absorbed therein, so that the noise is reduced while the watercraft is cruising at a wide range of speeds, or is at rest on the water surface. Further, in the case where water from behind the watercraft splashes toward the exhaust outlet, the closing portion of the sheet member protects the exhaust outlet by closing the same, thus preventing water ingress from the exhaust outlet into the engine.
Preferably, the personal watercraft may further comprise a press member for mounting the sheet member and the short pipe to the transom board, and the press member has a mounting portion for mounting the sheet member and the short pipe to the transom board from behind the body.
Preferably, the short pipe may be formed integrally with the press member. In this structure, the number of parts is reduced, and the seal between the short pipe and the press member and rigidity of these members are improved.
Preferably, the sheet member may have a closing portion larger than the exhaust outlet and capable of closing the exhaust outlet, a peripheral portion provided around the closing portion so as to be separated from the closing portion, and a connecting portion partially connecting the closing portion to the peripheral portion, and the short pipe may have a vent passage sized to permit the closing portion to swing rearwardly around the connecting portion.
Preferably, the mounting portion of the press member may be mounted to the transom board to mount the peripheral portion of the flexible sheet member.
Preferably, the connecting portion of the sheet member may be located at an upper portion of the closing portion. In this structure, when the exhaust gas is discharged, the closing portion is deformed around the upper portion by its exhaust pressure so as to swing around the upper portion away from the exhaust outlet, so that an exhaust passage is created. In this structure, since the closing portion of the sheet member is suspended from the upper portion, a reliable structure is achieved.
Preferably, the closing portion may be separated in an incomplete-circle shape by a slit from the peripheral portion of the sheet member except the connecting portion.
Preferably, the closing portion may be separated by a slit in a U-shape from the peripheral portion of the sheet member, except the connecting portion, the closing portion being substantially U-shaped with a lower portion formed by a semi-circular line and an upper portion formed by straight lines extending from the semi-circular line. In this structure, the length of the connecting portion can be set larger and durability can be thereby increased.
Preferably, the sheet member may be made of rubber. The sheet made of rubber has flexibility and durability.
The above and further objects and features of the invention will be more fully be apparent from the following detailed description with accompanying drawings.